Reflected across the x-axis, the function becomes
... g(x) = -f(x) = -20 +4x
This models the situation in which the car is driving in reverse, is accelerating (velocity is becoming less negative), and comes to a stop in 5 seconds.
Of the choices offered, the best seems to be ...
... b. the car immediately begins to accelerate at the same rate it had previously decelerated.